While natural fluctuations in water levels are normal, when lake levels drop and stay down, it raises a red flag. Lake Michigan’s water level changes naturally over time, just like the rest of the Great Lakes. Fed by precipitation, runoff, groundwater, and flow between the chain of Great Lakes, water levels fluctuate with the seasons. On a longer time scale, four- to seven-foot cycles between high and low occur approximately every 15 years.
In addition to this natural variation, locks, dams, and climate change are modifying these natural cycles, while other activities have permanently lowered lake levels. Much effort has been devoted to protecting the natural ebbs and flows of the Great Lakes since they are critical to the health of coastal habitats that support people and wildlife.
The levels of water in all of the Great Lakes are in constant flux. Rainwater and runoff feed water into the lakes while at the same time water flows from one lake to the next through connectors such as the St. Mary’s River. With the seasons, water freezes and thaws. As a result, research shows that lake levels fluctuate naturally over time, normally on 303 and 160-year cycles.
Human modifications to the Great Lakes and their connecting channels have drastically altered these natural cycles, resulting in some pronounced changes.
Dredging projects, where river channels are made deeper and/or wider for commercial navigation, have lowered Lake Michigan up to 20 inches since the 19th century. Similarly, engineering projects including historical modifications to the St. Clair River and the 19th century reversal of the Chicago River—aimed to keep waste out of Chicago’s drinking water supply—permanently altered lake levels.
Indirect factors impact lake levels, too. According to the Southern Lake Michigan Regional Water Supply Consortium, groundwater is replenishing slower than it did in the past due to “overuse and wasteful practices” on land. Since groundwater replenishes the Lake, less groundwater means less goes into the lake. The normal, annual average of water replenishment to Lake Michigan hovers at about 1 percent.
Now Great Lakes water levels face perhaps the toughest challenge yet: climate change. Most scientific models predict warmer and drier conditions in the upper Midwest. Although this may sound like more livable winters, what it means is that less water will freeze, less rain and snow will fall, and more water will evaporate. In all, scientists predict that climate factors may cause water levels in the Great Lakes to drop up to five feet—permanently—over the next hundred years.
So, what happens when human and climatic modifications change lake levels? Water levels drop and stay down. Organisms that depend on the water feel the repercussions of these permanent cycle changes. Coastal habitats depend on the consistent rhythm of the natural fluctuations—up to 90 percent of Great Lakes fish species rely on healthy coastal habitats at some point in their lifecycle.
But lake ecosystems and inhabitants aren’t the only ones that are affected. Changes to the natural ebb and flow can wreak havoc on other critical Great Lakes systems like coastal wetlands as well. Commercial and recreational boaters also feel the pinch of lower lake levels when they are forced to carry lighter loads or have trouble getting out of harbor.
The International Joint Commission, an agency that researches and recommends strategies to manage the Lakes for the Canadian and U.S. governments, is intensively studying the water levels of Lakes Superior, Michigan, and Huron. Although much study is being directed towards lake level changes and their effects, it may be years before we have full answers to these complex questions. In the meantime, the Great Lakes Water Resources Compact—a federal law and bi-national agreement finalized last year that mandates intense scrutiny for proposed new uses of lake water—was passed in 2008 and is already working towards protecting the Great Lakes from the impacts of human uses of water.
What You Can Do
- Conserve water in your home by decreasing the lengths of your shower, repairing leaky faucets, and installing water-saving fixtures. Hint: try these City of Chicago Water Conservation Tips.
- Calculate your current water use footprint and learn how to reduce it.
- Help slow global warming with climate change tips from the U.S. EPA website.
- Collect rainwater from your rooftop and use it to water your lawn, wash your car, or fill your pool. Learn how to collect your own rain with the City of Chicago’s Rain Barrel Initiative.
- Support government efforts to reduce water use locally and enhance the economy. Read more in a recent Alliance for the Great Lakes Report.
Written by Joel Brammeier, Alliance for the Great Lakes